Part III - Knowledges

This part tackles the different knowledge inputs into the assessments of the Intergovernmental Panel on Climate Change (IPCC), but also how the IPCC itself shapes knowledge products, and how and when these knowledges lead to controversy. Arthur C. Petersen (Chapter 12) assesses the disciplinary expert knowledges reflected in IPCC assessments, in particular those from the natural and social sciences, and shows how the IPCC’s work streams end up structuring and impacting the production of scientific and social scientific research more generally. Bianca van Bavel and colleagues (Chapter 13) considers the climate knowledges that are poorly assessed in IPCC reports, in particular Indigenous knowledge systems. They discuss some of the processes through which these systems could be better integrated in the assessment process. Hélène Guillemot (Chapter 14) considers the central role that climate models play in IPCC assessments, and their evolution over the various IPCC assessment cycles, while Béatrice Cointe (Chapter 15) offers a parallel assessment of IPCC scenarios and the dependence of these influential scenarios upon Integrated Assessment Models. Both chapters discuss how international communities of modelers orchestrate their work around IPCC assessment cycles. Finally, Shinichiro Asayama and colleagues (Chapter 16) examine the nature of the scientific and political controversies that the IPCC has faced over time and the role of the organisation in triggering or absorbing them. All chapters in this part emphasise the positive feedback loops that exist between the IPCC and different scientific and policy communities.

12 Disciplines

Arthur C. Petersen

Overview

The knowledge that is used in the assessments of the Intergovernmental Panel on Climate Change (IPCC) predominantly stems from a wide variety of academic disciplines. Given the high scientific and political profile of the IPCC, the production of knowledge in disciplines is impacted by the existence and dynamics of the IPCC assessment process. In some cases, the dynamics between academic disciplines and the IPCC is characterised by the presence of positive feedback loops, where the production of knowledge is structured and programmed by the IPCC. The subsequent findings then receive a preeminent role in later IPCC assessments, and so the cycle continues. It is important to critically reflect on these dynamics, in order to determine whether visions of climate change’s past, present, and future – for example, pathways for the climate change problem and its potential solutions, as far as they exist – have not been unduly constrained by the IPCC process. The IPCC runs the risk of unreflexively foregrounding some scientific and policy approaches at the expense of other approaches.

12.1 Introduction

Experts from different academic disciplines contribute to the IPCC via publications in the peer-reviewed literature and by being authors or reviewers in the IPCC assessment process. The IPCC reports’ Lead Authors have a powerful authority to decide on which bodies of academic literature from different disciplines are most relevant for their chapters. And they have to weigh their reliance on disciplinary knowledge against the use of highly relevant, but non-disciplinary, expert knowledge – for example from practitioners, or Indigenous knowledge holders. The role of the review process is to ensure that author teams do not ignore relevant bodies of literature and expertise (see Chapter 11). This chapter critically analyses with which disciplines the IPCC engages and how it does this.

Within the IPCC, an epistemological hierarchy can be seen to be at play between and within different disciplines. In the IPCC, the physical sciences have typically been regarded as sitting at the top (the ‘strongest’ type of knowledge), with biological and ecological sciences, engineering, and economics being in the middle, and qualitative social sciences and humanities residing at the bottom (the ‘weakest’ type of knowledge). An example of an epistemological hierarchy within disciplines is that in Working Group I (WGI) – dealing with the physical science basis – estimates from process-based models have typically been awarded a higher status than other types of estimates (e.g. those based on past observations), as will be illustrated later. Furthermore, the IPCC process itself is having an impact on the practices of scientific research – that is, on the development of disciplines themselves. For example, visions of future ‘solutions’ to climate change are propagated by the IPCC and are impacting research agendas (see Chapter 15).

This chapter first reviews the extant literature on how the IPCC has engaged disciplines from both natural sciences and social sciences and humanities. Subsequently, the attention shifts to influences in the opposite direction – that is, the extent to which the IPCC has had an impact on the production of knowledge in disciplines.

12.2 Engagement with Natural Sciences

Climate (later Earth system) models have always been important within the IPCC (see Chapter 14). Bjuström and Polk (2011) have shown that the natural sciences, and in particular the earth sciences, have dominated the early assessment reports. In the 1990s, the use of complex climate models dominated the work of WGI (e.g. Petersen, 2000, [2006] 2012). For example, enacting an epistemological hierarchy, the IPCC modellers in WGI initially downplayed palaeoclimatological knowledge and studies on abrupt climate change in the past (Demeritt, 2001). It took until the Fourth Assessment Report (AR4) (2007) before there was a marked increase in the visibility and importance of palaeoclimate expertise within WGI assessments (Caseldine et al., 2010). But by that time the IPCC was still not ready to include expert judgements on rapid sea-level rise, which are partially based on palaeoclimatic expertise, instead preferring model-based assessments (see Box 12.1).

Box 12.1 Expert judgement versus models on rapid sea-level rise

For decades, there have been palaeoclimatological studies of rapid sea-level rise in the distant past, including periods with several metres of sea-level rise in the timeframe of a century, which could provide useful information to assess future sea-level rise. But it has taken the IPCC six cycles of assessment, over 30 years, to integrate the results of these studies and provide – with the August 2021 release of the AR6 WGI report – a plausible upper estimate of sea-level rise in 2100 of 2 metres. (This is a much higher number than the ‘likely’ range, taking into account possible ice sheet instability.) More than 14 years earlier, in the IPCC WGI AR4 plenary session, I – as a Dutch government delegate – had not been able to convince the respective Lead Authors to provide their expert judgement, based on inputs from several disciplines including palaeoclimatology, as opposed to results from models with known limitations. This is evidenced by my diary entry, published shortly after the plenary:

Early in the afternoon [of Wednesday 31 January 2007, acp] I have a conversation with two authors on the maximum height of the sea level rise in 2100. According to model projections the maximum sea level rise is 59 centimetres. This number does not include an estimate for the possible accelerated melting of Greenland and Antarctica. It seems that scientists really do not know what will happen with Greenland and Antarctica. But a possible accelerated meltdown could lead to a sea level rise of more than one metre. Should we mention that, without being able to say something about the probability? Or should we just say that we cannot identify an upper limit?

The authors propose a text that now makes clear that we cannot give an upper limit. That is better than it was, but I still find it unsatisfactory. For readers it would be nice if we could give an indication of how much the sea level could maximally rise. But as IPCC we have a responsibility to say what is and is not known. The text on the ignorance regarding the upper limit appears acceptable to all delegations. Also to the Dutch – I do not push this further.

(Petersen, 2007: 21)

O’Reilly et al. (2012) later found that a (re-)organisation of chapters, assigning a central role to sea-level modellers, had made it harder to include an estimate for the upper limit of sea-level rise due to ice cap melting by 2100, in part because it did not consider information from palaeoclimatological studies. In a later publication, it was demonstrated how the difficulties of modelling accelerated meltdown of ice sheets had led to underestimates since the IPCC’s beginnings (Oppenheimer et al., 2019). And due to an epistemological hierarchy that favoured process-based models over past observations it was hard to include palaeoclimatological evidence in the IPCC’s expert judgement on the upper limit of sea-level rise.

More generally, there has been a predominance within the IPCC of quantitative natural scientific knowledge. For example, ‘attribution’ studies have been very important, and increasingly so in recent assessment rounds. Initially, the attribution of global temperature change to human influences was the main focus; nowadays, attribution science has broadened to quantitatively attributing ecosystem and human system changes (in WGII) and individual weather events (in WGI) to human-induced climate change.

12.3 Engagement with Social Sciences and Humanities

Social sciences and humanities scholarship has gradually been drawn in over the course of the different IPCC assessment cycles. Nevertheless, the relative autonomy of the separate WGs, combined with differences in their respective disciplinary mixes, has led social scientists to conclude that the interdisciplinary integration necessary for tackling climate change has been hindered by a ‘unidisciplinary structure of work’ (Godal, 2003). For example, in the context of designing greenhouse gas indices – which allow one to compare the warming effects of different greenhouse gases – the WG structure, with the exclusion of social science disciplines in WGI, made it harder to draw appropriately on existing interdisciplinary work to integrate damages and costs in greenhouse gas indices (on integration between WGs see Chapter 18). Another straightforward example of the lack of disciplinary interaction between different social scientific disciplines within the IPCC is that between the meta-policy domains of adaptation and mitigation, since these domains are covered by different WGs.

Epistemological hierarchies are evident both between WGs – with generally more authority being attributed to WGI – and within WGs. The Third Assessment Report (AR3) Report (2001) aimed to include a larger range of social sciences, but with mixed results (Rayner & Malone, 1998). AR4 (2007) was still weak on social science, which led to calls to the IPCC, as well as to the research community, to produce more studies on citizen participation, on culture, ethics and religion, and on the incorporation of more diverse actors (e.g. Hiramatsu et al., 2008). Economics has been predominant among the social sciences that have been mobilised by the IPCC (Yearley, 2009). It can certainly be argued that the IPCC engages less with social science disciplines than is possible or desirable. On the one hand, the IPCC is confronted with many questions that social science can address. On the other hand, it is also important to realise that some social science disciplines, such as political science, whilst important, do not address climate change as a central topic. More generally, because of ontological plurality in the social sciences, it can be harder to organise social-science knowledge compared to natural science (Victor, 2015). It also has not been easy to integrate the first philosophers into the IPCC process in the Fifth Assessment Report (AR5), as was evidenced by their different modes of working, both in the draft writing and in the plenaries. For example, their purview was typically not bound to assessing only the last few years of literature (Broome, 2020).

A major effect of the limited engagement with social science by the IPCC has been its poverty in terms of socio-technical visions. It has long been clear that the IPCC’s integration of the topic of sustainable development has been limited (Najam et al., 2003) and that futures research has been only very modestly represented (Nordlund, 2008). The various sets of scenarios that have been constructed by, or for, the IPCC have also been constrained and focused on extreme ‘business-as-usual’ scenarios (Demeritt, 2001; Pielke & Ritchie, 2021). This critique parallels a growing prominence of integrated assessment modelling (IAM) analyses in subsequent IPCC reports (see Chapter 15). This has several causes, ranging from the particular features of these modelling approaches – including their flexibility, breadth, and hybridity – that allowed them an ‘anchoring’ function between WGs, to proactive behaviours by those involved in the discipline of IAM (van Beek et al., 2020a). This has had consequences. For example, Integrated Assessment Models do not pay much (if any) attention to the impacts of policies on land use, food security, human rights and investment costs, and the wider politics of developing new plantations and infrastructures. One consequence of this has been a large global reliance in the IPCC’s projections of future development pathways – certainly since AR5 – on Bio-Energy Carbon Capture and Storage (BECCS) to stay below or return to global average temperature increases of 1.5 °C or 2 °C by 2100.

Note also that the IPCC does not only rely on knowledge deriving from academic disciplines but also – although until recently to a very limited extent – on knowledge that stems from elsewhere, for example various types of practitioners including legal experts or Indigenous knowledge holders. For example, Viner and Howarth (2014) argue that knowledge on climate adaptation from practitioners is relevant for IPCC reports and should be included centrally. And an answer is needed to the critique that expertise on Indigenous peoples has been brought in only obliquely and problematically through ‘the narrative of pending catastrophe, the tropes of cultural loss and the urgent need for pan-global solutions’ (Ford et al., 2016: 351; see Chapter 13).

12.4 Impact on Disciplines

Far from merely assessing existing published knowledge, the IPCC – directly or indirectly – shapes the types of questions research communities investigate and therefore has an active presence in determining what research gets funded. The IPCC’s engagement with disciplines has an impact on their development. This becomes evident from the pervasiveness and dominance in the academic literature of a structural linearity of knowledge which moves from geoscience to impact, adaptation and mitigation, mirroring the IPCC WG structure (see, for example, the presentations at the Copenhagen Congress in 2009; O’Neill et al., 2010). IPCC reports are also regularly cited in the primary scientific literature, with a skewness towards geophysical sciences, although this skewness is gradually decreasing as the IPCC’s assessments increasingly impact on the shaping of other disciplines (Vasileiadou et al., 2011).

Evolving policy needs, embodied in IPCC assessments, create selection mechanisms for climate science (Vasileiadou et al., 2011). The IPCC is regularly asked to treat subjects for which there is not yet a strong underlying research base (see Chapter 5 on the reports process), especially in the social sciences. This has led to calls for bringing together descriptive and interpretive social science methods to usefully tackle questions on, for instance, vulnerability and adaptation (Malone & Rayner, 2001).

Early studies on the IPCC already observed that WGI anticipated reductions in scientific uncertainty about climate change that would come through particular national and international research programmes (Shackley & Wynne, 1996). This led to the introduction of new subjects in climate science research as a direct consequence of IPCC discussions (Shackley & Wynne, 1997). For example, funding for palaeoclimatological research has been framed in terms of its expected contribution to the testing of complex models necessary for IPCC assessments. In the 1990s, IPCC-influenced funding was also made available for reducing physical-science uncertainties, but not so much for studying uncertainties pertaining to the human dimensions of climate change, especially those that do not connect well to a natural science frame (Demeritt, 2001). Finally, in past decades, the main impetus behind climate modelling and model intercomparison projects (see Chapter 14) has come from the IPCC assessment process (Yearley, 2009). Funding opportunities for palaeoclimate research have increased more recently with the growing importance of palaeoclimate reconstructions within the IPCC (Caseldine et al., 2010).

A direct impact on knowledge generation of participation in the IPCC has been identified by social scientists, namely how IPCC authors flag gaps in the published literature and then pursue the called-for new research themselves in order to fill those gaps. For example, in the climate-mitigation field, individuals and institutions are organising their research, collaboration and publication strategies around the assessment of knowledge in IPCC reports. This makes climate-mitigation research, as a discipline, effectively dependent on the IPCC (Hughes & Paterson, 2017). The 2015 UNFCCC request to produce a special report on 1.5 °C signalled a shift from ‘science-driven co-production’ to ‘policy-driven co-production’ which has been most visible in the production of IAMs and associated scenarios – there has been a sharp increase in IAM publications ahead of each cycle of IPCC reports (van Beek et al., 2020a). The centrality of the IAM community to the IPCC’s mapping of mitigation options – such as taking 2 °C and 1.5 °C as targets for pathway modelling – has constrained the research questions being addressed. In a circuitous way, this feedback loop has led to the prominence of BECCS among potential climate-change measures (Low & Schäfer, 2020). In sum, the IPCC, with its substantial involvement in emissions scenario production and use, has had a central role in orchestrating the scientific literature on climate change. Some important questions have not therefore been researched by the academic community that might otherwise have been (Hulme, 2016).

From a systems perspective, positive feedback loops can be identified. For instance, being a lead author leads to advantages in scholarly publishing, which leads such authors to become more influential within the IPCC, and so on (Hughes & Paterson, 2017). This is another instantiation of the ‘Matthew effect’ – the rich getting richer and the poor getting poorer – that has been studied in the sociology of science since the 1960s. At the institutional level, the IPCC plays a major role in the orientation, rhythm and domain of applicability of some fields of climate research (Cointe et al., 2019). For example, the current prominence of IAMs to explore low-carbon futures is a result of complex historic science–policy dynamics involving the IPCC, a central part of this being IAMs’ anchoring of relationships among the three IPCC WGs (van Beek et al., 2020a). A similar positive feedback loop had also been observed earlier in the case of complex climate models (e.g. Petersen, 2000, [2006] 2012; Demeritt, 2001; Yearley, 2009).

On the other hand, there have also been calls for the IPCC to exercise a larger impact on academic disciplines. The lack of integration of disciplinary knowledge within the IPCC, beyond the natural sciences and economics, is partly related to the way academic institutions are organised around separate disciplines (Bjurström & Polk, 2011). For some scholars, a successful transformation within the social sciences and humanities towards systematic and integrated knowledge generation is seen as needed to help increase the policy relevance of IPCC assessments (Minx et al., 2017). The recent establishment in universities of numerous ‘Schools of Sustainability’ and similar academic units can be seen to contribute to this goal.

12.5 Achievements and Challenges

The IPCC, through its rigorous procedures, has been able to successfully create credible assessments of the evolving state of expert knowledge on climate change. However, there have been some drawbacks to the way that the IPCC has relied on academic disciplines. For example, the IPCC’s focus on peer-reviewed publications has devalued other types of less academically formalised expert knowledge, such as practitioner and engineering expertise and legal reports, or Indigenous knowledge (Beck & Forsyth, 2015).

I suggest that major changes are needed in the way the IPCC engages with disciplinary and other expert knowledge. The information needs of decision-makers and practitioners around the world are varied and increasingly urgent. Yet, as these needs have expanded, there has been a widening gap between what most IPCC authors understand to be useful information and what decision-makers see as informative (Petersen et al., 2015). It has been argued that the addition of a fourth WG on ‘historical, cultural, and social contexts’ could assist in re-framing climate change as an ethical, cultural and political phenomenon. This could counter the observed epistemological hierarchy, with biases in the existing WGs towards physical and economic sciences (O’Neill et al., 2010).

However, I judge that this has only limited potential of success in terms of integration with the other IPCC WGs and its ability to function within the UN system. Since governments want to control the IPCC’s statements about social behaviour, or statements that implicate policy choices, it is mostly politically non-controversial ‘high confidence’ statements that make it into the Summaries for Policymakers. Such statements are more likely to emerge from ‘positivist’ disciplines than from interpretative ones. A parallel process to the IPCC – but non-governmental – would be needed to address controversial topics such as how best to design international agreements or how to govern the use of geoengineering technologies (Victor, 2015).

Finally, the presence of positive feedback loops described in this chapter not only shows the presence of a potential conflict of interest – with for instance Lead Authors filling the research gaps that they themselves identify – but also highlights the fact that the IPCC has now increasingly become self-referential. This raises questions about the notion of the IPCC’s ‘policy relevance’. More specifically, who decides what policy relevance is? There is a danger that researchers – finding eager receptors in particular policymakers involved in UNFCCC processes – are deciding what disciplines are policy-relevant for IPCC assessments. The IPCC should find ways to become more reflexive about this issue, while a wide set of decision-makers should seek to construct a larger ecosystem of science–policy institutions that meet their practical needs.

13 Indigenous Knowledge Systems

Bianca van Bavel , Joanna Petrasek MacDonald and Dalee Sambo Dorough

Overview

The Intergovernmental Panel on Climate Change (IPCC) has begun to acknowledge, albeit slowly, the importance of Indigenous knowledge (IK) systems in contributing to understandings of climate change and effective climate action. Yet Indigenous Peoples (IPs) and IK systems remain largely excluded and marginalised from the IPCC global assessment reports. IPCC scientists and leaders have a unique and specific obligation to IK systems that does not extend to other knowledge systems. IK is the knowledge of rights holders and therefore acknowledging and respecting the self-determination of IPs over their knowledge – including how it is used, interpreted and synthesized – is imperative. There are examples of IPs organising themselves in other international spaces that could inform how the IPCC can approach a stronger, more durable engagement with IPs. Perhaps the ultimate challenge for the IPCC is that when bringing IK systems together with other knowledge systems, the framing of evidence must reflect the diversity of these distinct and discrete ways of knowing. Examples from the lived experience of the Inuit Circumpolar Council (ICC) in engaging with the IPCC demonstrate diverse channels for engagement, yet significant limitations persist.

13.1 Introduction

As it stands, the IPCC ‘knowledge base’ consists largely of peer-reviewed and internationally available academic literature with some selected non-peer reviewed – so-called ‘grey’ – literature (see Chapter 12). Given the nature and scope of the peer-review publication process, this translates into assessing evidence predominantly through a Western scientific lens. Widening the knowledge base is not just about including more diverse peer-reviewed literature. It is about engaging with diverse knowledge systems and forms of evidence originating outside a scientific system of understanding, crucial among these being IK systems.

Excluding or failing to adequately and appropriately engage with IK systems results in a failure to capture in-depth and extensive evidence that could (i) significantly enhance the understanding of environmental, biophysical and climatic systems; (ii) provide crucial information about the interconnections between humans, more-than-humans and the environment, and (iii) strengthen the knowledge base in such a way that could help to advance evidence-based climate policy and create better-informed rigorous climate action responsive to all, including IPs. This chapter makes a case for widening the IPCC’s knowledge base to include IK systems. But it also outlines how this might be done by discussing what it means to ethically and equitably engage with IK systems.¹ To do this we draw both from published academic literature and from lived experience of the IPCC’s exclusive processes and limitations to its knowledge base.

13.2 IK Systems

IK systems have been largely excluded from IPCC reports to date and from climate research broadly (Ford et al., 2012; Smith & Sharp, 2012; Ford et al., 2016; van Bavel, 2021). However, IK systems have been recognised as essential to understanding the environment and human-environment relationships, and to developing solutions to mitigate and adapt to the climate crisis (e.g. Laidler et al., 2011; Nalau et al., 2018; IPCC, 2019g; Sawatzky et al., 2020). Furthermore, IPs live in environments and ecosystems that are often heavily impacted by climate change and therefore have extensive lived experience and an intimate knowledge of climate change (Maldonado et al., 2016; Savo et al., 2016; Forest Peoples Programme et al., 2020). Indeed, the profound relationship that IPs have with their lands, territories and resources – and their collective rights to their lands, territories and resources – is a unique and unparalleled connection. It is therefore essential for the IPCC to make linkages between IK systems and impacts of climate change on Indigenous lands.

IPs own, protect, manage or have tenure rights to more than a quarter of the Earth’s land territory, comprising 40 per cent of all protected land and ecologically conserved landscapes with high biodiversity and carbon storage (Garnett et al., 2018; Forest Peoples Programme et al., 2020). This intimate knowledge and stewardship expands the understanding of the impacts of climate change, and how to respond to them. IK has been defined in many ways and will not be defined in one way here; rather, it is essential to recognise the various definitions of IK, such as that offered by the ICC² (see Box 13.1). We note that IPs have the right to define IK as they understand and engage with their own knowledge.

Box 13.1 One of many definitions of Indigenous knowledge

Inuit Circumpolar Council (2013)

Indigenous knowledge is a systematic way of thinking applied to phenomena across biological, physical, cultural and spiritual systems. It includes insights based on evidence acquired through direct and long-term experiences and extensive and multigenerational observations, lessons and skills. It has developed over millennia and is still developing in a living process, including knowledge acquired today and in the future, and it is passed on from generation to generation. Under this definition, IK goes beyond observations and ecological knowledge, offering a unique ‘way of knowing’. This knowledge can identify research needs and be applied to them, which will ultimately inform decision makers. There is a need to utilise both Indigenous and scientific Knowledge. Both ways of knowing will benefit the people, land, water, air, and animals within the Arctic.

Regardless of the term or definition, IK is the knowledge of rights holders. IK systems are therefore tied to Indigenous rights and any engagement with IK systems requires a rights framework or rights-based approach. IK systems cannot be taken out of the specific cultural context from which they emerge. It is also crucial to recognise that IK systems and Indigenous languages are inextricably connected. Serious rights safeguards are imperative in relation to IK systems³ and such safeguards must be recognised and respected. Article 31 of the UN Declaration on the Rights of Indigenous Peoples affirms ‘the right to maintain, control, protect and develop their intellectual property’ (emphasis added). This must be understood as directly linked to exercising the elements of the right to free, prior and informed consent – here, the term ‘control’ in its plain meaning suggests that the peoples concerned have power over, to influence, manage, restrain, limit or prevent something from taking place (United Nations, 2007). Article 31 must also be read in the context of the whole of the instrument and all the interrelated rights affirmed therein. A rights-based approach means acknowledging and respecting the self-determination of IPs, their governance systems, their right to define their knowledge systems and to be equal partners in knowledge translation and mobilisation. It also means understanding IPs’ rights to represent their people in regional, national and international processes, whether this be knowledge production, knowledge assessments or policy development. In applying an Indigenous worldview, knowledge cannot be separated from governance. To capture the richness and depth that IK systems can offer, Western models of knowledge production, synthesis and decision-making should welcome IPs and recognise them as fellow experts, decision-makers and distinct knowledge holders.

Lastly, it is important to understand that IPs are well organised in international climate spaces. IPs have self-organised to effectively and directly participate in various international systems including the International Union for the Conservation of Nature (IUCN), the Convention on Biological Diversity (CBD), and the UN Framework Convention on Climate Change (UNFCCC). While the organisation of IPs around each system varies in operation and membership, the structural framework and core principles remain consistent. In dealing with such international bodies, IPs are formally recognised within the UN system and are engaged and organised into seven UN socio-cultural regions – Africa, Asia, Latin America and the Caribbean, Russia, the Arctic, the Pacific, and North America. IPs in these regions coordinate regionally to discuss and determine shared interests and priorities. They then come together under one Indigenous body – for example, for the UNFCCC, IPs gather under the International Indigenous Peoples Forum on Climate Change (IIPFCC), also referred to as the IP caucus⁴ – to build consensus around shared Indigenous positions and messages.

These bodies and organisational structures have been in place for decades and are well recognised. They uphold principles of diversity, inclusivity, collaboration, fluidity, and respect for local and regional governance structures. IPs can engage with the Indigenous body while at the same time engage with advocacy and actions specific to their organisation, country, priorities, strategies or region. Recognising the centuries-old debates concerning the status, rights and roles of IPs and the historical antecedents of IPs as objects and subjects of international law, the world community has embraced IPs. Yet, challenges such as the engagement of IK remain. It is therefore important to recognise these structures because they demonstrate IPs’ in-depth knowledge and experience in engaging with international climate processes and are exemplary in respecting self-determination. There is extensive expertise within and readiness from IPs to engage with the IPCC and examples of how to facilitate this (see Section 13.7).

13.3 Engaging with IK Systems in Equitable and Ethical Ways

Widening the knowledge base to ethically and equitably include IK systems in the IPCC is two pronged. The first important element is to engage with IPs directly and to provide opportunities for partnership and direct participation in the IPCC process. Responsible engagement includes processes of partnership and participation that are initiated in mutual agreement with or by IPs (David-Chavez & Gavin, 2018). This is contrary to the extractive models of engagement often applied when attempting to access IK systems externally from Western scientific contexts of research and evidence assessment. Developing relationships with IPs and organisations is one initial effort that will aim to ensure IK systems are present in IPCC assessments.

The other crucial element is ensuring that the ongoing machine of knowledge production that feeds into the IPCC prioritises the co-production of knowledge. Knowledge co-production is a process in which multiple distinct and separate paradigms are applied simultaneously at all stages of knowledge generation (Tengö et al., 2014; Johnson et al., 2016; Berkes, 2018; Hill et al., 2020). While being considered together in this generative process of co-production, the integrity and quality of each knowledge system is still valued as it continues to engage in its independent production processes (IPCC, 2019f; their Fig. CB4.1). According to a recent report produced by the ICC, aiming for genuine co-production of knowledge is a crucial part of ethically and equitably engaging with IK systems. It requires essential elements of trust, respect and relationship, as well as full acceptance of agreed values (ICC, 2021). Further guidance towards genuine co-production processes involves acknowledging IK ‘as a unique knowledge system that comes with its own evaluation and validation processes’ (ICC, 2021: 20). This guidance extends to the IPCC assessment process and its synthesis of a diverse knowledge base and highlights the existing tensions between fundamentally different knowledge-handling processes that must be recognised and resolved for new knowledge to be co-produced.

Research assessing how IK has been used as evidence to shape IPCC assessments – from the Fourth (AR4) to the Sixth Assessment Report (AR6) – has demonstrated that, despite an increase in Indigenous-focused content over time, the IPCC process has no established procedures or guidance for ethically and equitably engaging with IK systems, especially where it is highly relevant (Ford et al., 2012, 2016; Smith & Sharp, 2012; van Bavel, 2021). Furthermore, the underlying principles and procedures that guide IPCC assessments have been shown to actively restrict the knowledge base from equitably and ethically engaging with IK systems (van Bavel, 2021). Here, an excerpt taken from publicly available IPCC expert reviewer comments also reveals some of the challenges encountered when working within the existing IPCC assessment process:

It is somewhat difficult to use ‘published’ IK – first of all because very little is published, second, because it can easily be taken out of context and be misinterpreted, since it is very complex. The context/analysis should ideally always be confirmed by the knowledge holders – Expert Reviewer 22590 SROCC

IPs highlight protocols and methodologies that belong to the worldviews and paradigms of IK systems (e.g. Kovach, 2009; Inuit Tapiriit Kanatami, 2018; Whyte, 2018; ICC, 2021). They can offer a process, outside of Western scientific forms of validation, for widening the knowledge base through knowledge co-production (e.g. Tengö et al., 2014; Parsons et al., 2016). Multiple, distinct and separate knowledges coming together requires a framing of evidence that reflects such diversity – including fundamental differences in epistemology, ontology, methodology and axiology (see Chapter 18). Critically, this need for reforming the assessment process to widen the knowledge base has been echoed by Indigenous persons and organisations navigating their own engagement with the IPCC. One such organisation is the ICC, which has called for and exemplified the importance of a two-pronged approach to widening the knowledge base. This is through direct participation, engagement and partnership of IPs in the IPCC process, and through prioritising the co-production of knowledge. ICC has shared this message and embodied this approach in various ways including as an expert reviewer, as a contributing author, as a member of a government’s delegation to plenary sessions, and most recently as an official observer.

13.4 IPs and IPs Organisations as Expert Reviewers

The existing IPCC review process plays a significant role in engaging the IPCC’s knowledge claims through experts beyond academia, including those from government, non-government and industry (see Chapters 10 and 11). As an expert reviewer, the ICC has made substantial comments and fed directly into IPCC assessments during this review process. The extent to which these comments are addressed has varied, but has allowed for the ICC to consistently call for more engagement with IK systems and qualify what that engagement should look like. Despite the significant demand on time and resources that is required to adequately complete the IPCC review process, ICC has continuously provided expert Indigenous-specific input and analysis on how the various reports have used IK systems. It has also provided detailed expert advice on appropriate language, framing, literature and other source materials. For example, it has ensured that when IK is introduced in the Summary for Policymakers it is alongside concepts of Indigenous rights and self-determination within the research and evidence assessment process (Expert Reviewer 3088, SROCC). As an expert reviewer, ICC has flagged the absence of Indigenous authors and emphasised in numerous review processes the importance of partnership and direct participation. It has called for genuine opportunities to contribute co-authored content, especially where the IPCC refers to the work and knowledge of ICC and other IPs:

Ideally, Indigenous knowledge holders should participate in the development of these reports so that they stand as an example of HOW to be engaging with Indigenous knowledge … there are many communities and individuals from this population whose voices, knowledge, and experience would have strengthened the writing of this report had they been brought in from the beginning – Expert Reviewer 9604, SR1.5

13.5 Indigenous Authorship

During the most recent IPCC assessment cycle, ICC has worked with an IPCC author who understands what it means to ethically and equitably engage with IK systems. This author has sought to provide more meaningful opportunities to include Indigenous voices and knowledge in IPCC assessments. Through this relationship, ICC has contributed text to the IPCC SROCC and IPCC AR6 WGII Polar Regions Cross-chapter Paper. Ensuring the integrity and robustness of a contribution can be very challenging when facing word limits, restrictions to peer-reviewed sources, requirements to fit into a Western framing, and comments from other authors, expert reviewers or government representatives who do not understand IK systems, IPs or Indigenous rights. In addition, as with the review process, authorship requires allotting staff time and resources to IPCC work, often without having allocated funding for this work. However, this opportunity to contribute has provided ICC greater insight into the process and allowed for a stronger understanding of where to find intersections and common points of convergence that can facilitate the utilisation of IK systems. Including Indigenous authors in the IPCC reports is certainly one step towards meaningful engagement. Continuing to include and support Indigenous authors should be a priority for the IPCC (Ford et al., 2012).

13.6 IPs as Part of a Member Government Delegation

The ICC has also been invited to join the Canadian delegation at Panel’s plenary meetings. As part of the Canadian delegation, ICC can participate in the final approval of reports, voice concerns that have not been addressed in the review process, and request changes to wording to ensure respectful and appropriate framing of IK systems and Indigenous perspectives. Support from governments by making space for Indigenous representation on the delegation is a significant step in the right direction. Yet Indigenous participation in this capacity remains limited and ultimately IPs should have their own autonomous and equal seat at the table. A step in this direction occurred in February 2020 when ICC was granted formal observer status to the IPCC (see Chapter 10). This is the first time an Indigenous Peoples Organisation (IPO) has been recognised as a formal observer and may provide new opportunities for engagement. ICC can now fully participate in its own right and represent itself at plenary sessions and when interacting with the Panel, the Bureau and the Technical Support Units. Observer status also may be useful for ICC to contribute to training workshops or expert meetings on the topic of IK systems. The absence of other observer IPOs further points to the lack of examples of IPOs intersecting or engaging with the IPCC.

13.7 Achievements and Challenges

Recognising that there are many ways of knowing – which must be considered together to inform the transformation of our understandings of climate change – is a recent awakening in the IPCC. We can trace the evolution of the treatment of IK systems in IPCC reports. This started with simply the recognition of IK systems as sources of knowledge in their own right, to having representations of IK in reports – albeit sometimes through inappropriate means – to seeing original contributions from an IPO, to having the first IPO accepted as an observer. We recognise that these are fledgling efforts from a regrettably small body of examples. And yet, there is the expertise, will and desire from within IPOs, including the ICC, to effectively and meaningfully engage with the IPCC process to ensure IK systems are included equitably and ethically within the knowledge base.

True transformation towards equitable and ethical engagement of IK systems and IPs requires going beyond fledgling practices of engagement. It requires changing the current paradigm, framing of evidence, and developing processes of the IPCC to reflect the diversity between and within knowledge systems and co-produce the transformative understandings of climate change needed today. Starting points would be having IPOs as full members of the IPCC and Indigenous representation in the Bureau; supporting Indigenous authorship/leadership early and often in the assessment cycle; recognising Indigenous peer-reviewed processes; and citing Indigenous-led materials in reports. There are many challenges and tensions, especially within the academic world, that restrict such transformation, some of which have been characterised in this chapter. It is not an easy task and the IPCC remains in the infancy of this unchartered territory. Yet engaging and mainstreaming IK systems in assessments like the IPCC perhaps offers a way forward for their adoption of new processes, paradigms and understandings. Certainly IPOs such as the ICC deem their engagement efforts worthwhile, despite the challenges and the glacier-paced change. Indeed, the benefits of being involved in the IPCC process and championing knowledge co-production and transformation, to the extent possible, will always outweigh the costs of time and resources because Indigenous lives, cultural integrity, ways of life and knowledge systems are at stake.

The extraordinary developments in favour of IPs within the field of international human rights law at the UN, Organisation of American States (OAS), International Labour Organisation (ILO), and elsewhere, suggests that the IPCC may have a responsibility to prioritise and value the ethical and equitable engagement of IK systems that does not extend to other knowledge systems. Here, we refer to the unique and specific set of obligations to understand Indigenous perspectives and worldviews, engage with IK systems and rights holders, and co-produce knowledge. This includes IPCC scientists and leaders questioning their assumptions, perspectives and approaches to knowledge production. To date, the burden of furthering increased understanding between IK systems and science has largely fallen on the shoulders of IPs and Indigenous academics. Such individuals understand the distinct cultural context of the Indigenous world, but they have been trained in the Western or non-Indigenous academic realm and understand both systems. These individuals who can act as bridges are rare, but have been essential in making these important connections (cf. multi-positional thematic bridges described in Chapter 18).

Beyond the IPCC, there are various bodies and mechanisms that offer opportunities from which the IPCC can learn about facilitating equitable and ethical engagement with IK holders and IK systems. Again, this is being done through Indigenous partnership and direct participation as well as prioritising the co-production of knowledge. For example: the Facilitative Working Group of the Local Communities and Indigenous Peoples Platform (LCIPP)⁵ under the UNFCCC, the UN Permanent Forum on Indigenous Issues (UNPFII)⁶, the Arctic Council⁷, as well as the IIPFCC (see Section 13.2). These are examples to learn from, but these bodies also continue to be challenged with fully embodying the equitable and ethical engagement of IK systems and co-production of knowledge in its fullest and truest form. IPOs like the ICC continue to work in these spaces to encourage and cultivate an understanding of IK systems. An expansive understanding of IPs based on their relationship with their lands, territories and resources can never be captured by Western science. The IPCC must strive to make its assessment processes ethical and equitable in a way that has relevance and validity for IPs, in Indigenous contexts. This could have resounding reciprocal benefits for climate research, policy and practice, as well as enhancing the recognition of IPs and implementation of their distinct rights globally.

14 Climate Models

Hélène Guillemot

Overview

Climate computer models are irreplaceable scientific tools to study the climate system and to allow projections of future climate change. They play a major role in the assessment reports of the Intergovernmental Panel on Climate Change (IPCC), underpinning palaeoclimate reconstructions, attribution studies, scenarios of future climate change, and concepts such as climate sensitivity and carbon budgets. While models have greatly contributed to the construction of climate change as a global problem, they are also influenced by political expectations. Models have their limits, they never escape uncertainties, and they receive criticisms, in particular for their hegemonic role in climate science. And yet climate models and their simulations of past, present and future climates, coordinated via an efficient model intercomparison project, have greatly contributed to the IPCC’s epistemic credibility and authority.

14.1 Introduction

The role of models in IPCC assessment reports cannot be overestimated. Models provide the core content of the IPCC’s reports; all assessment reports and their Summaries for Policymakers (SPMs) are illustrated by figures, graphs and maps based on the outputs of climate models. By providing climate simulations that made it possible to distinguish between anthropogenic and natural influences on twentieth-century climate, from the IPCC’s Third Assessment Report (AR3, in 2001) onwards, climate models were central for attributing observed climate change to anthropogenic greenhouse gas emissions with high confidence. Models therefore have a political role. They affirm the reality, form and intensity of climate change, but they also shape the IPCC’s particular conception of climate change with which governments engage. Conversely, the development of models and the organisation of climate modelling on an international scale has been in large part driven by the need to produce future climate projections for the IPCC.

In this chapter, I explain how climate models are constituted and how they have evolved and become essential instruments for predicting global climate change. I show how the models and scenarios used by the IPCC have been the target of attacks by climate sceptics, have been subject to critical scrutiny by social scientists, and aroused debates among climatologists about research biases, inadequacies and research strategies. I show how the modelling community has organised itself internationally to make climate simulations comparable by building a powerful ‘knowledge infrastructure’ (Edwards, 2010), the Coupled Model Intercomparison Project (CMIP). Finally, I return to the achievements of climate models and their limitations and ask what their new role could be in shaping future directions for the IPCC. The chapter focuses exclusively on climate models (see Box 14.1) and does not consider a different genre of models – Integrated Assessment Models (IAMs) – which are also central to the IPCC’s work; these are discussed in Chapter 15.

Box 14.1 Varieties of numerical climate models

A wide range of numerical models – i.e., programs run on computers to produce numerical simulations – are used to study the climate system and climate change across multiple temporal and spatial scales.

• GCM: General Circulation Model – or, more recently, Global Climate Model. GCMs are computer programs representing the evolution of the atmosphere. They build on the fundamental laws of physics that govern atmospheric dynamics and on more empirical representations of the other processes affecting the atmosphere (absorption of solar radiation, clouds and so on). GCMs are used on a daily basis for weather forecasts, and to simulate the climate over several decades, centuries or millennia – these long simulations being analysed in statistical terms.

• AOGCM: Atmosphere-Ocean coupled General Circulation Model. AOGCMs are numerical models consisting of an atmospheric general circulation model coupled with an ocean circulation model – both based on the laws of fluid dynamics.

• ESM: Earth System Model. ESMs seek to simulate all relevant aspects of the Earth system and its physical, chemical and biological processes. In practice, ESMs are atmosphere-ocean coupled models incorporating biogeochemical processes such as the carbon cycle. ESMs can also include models of dynamic vegetation, atmospheric chemistry, ocean biogeochemistry, and continental ice sheets.

• EMIC: Earth System Models of Intermediate Complexity. EMICs are simplified models compared to ESMs. They have lower spatial resolution and include processes in a more parameterised form. EMICs are used to investigate the climate on long timescales, for example, for simulations of palaeoclimates.

• IAM: Integrated Assessment Model. IAMs are large-scale models composed of modules representing environmental, technological, and human systems in a single integrated framework. They model the evolution of the interaction between these systems by integrating contributions from various disciplines (environmental sciences, economics, engineering and so on) to produce quantified scenarios of global socio-economic developments.

• Simple models and emulators: Simple models and emulators are heavily parametrised models, quick to run on laptops or even iphones, and tuned to reproduce the responses of more complex models. Emulators in particular are used to transfer knowledge between the IPCC WGI and other Working Groups (WGs).

14.2 Instruments of Globalisation and Prediction

Climate models, originally called General Circulation Models (GCMs), are numerical programs run on computers to produce simulations of the evolution of the atmosphere. The atmosphere is represented by a three-dimensional grid and the computer calculates for each cell and at each time step the variables characterising the atmospheric state (temperature, pressure, wind, humidity and so on) by solving algorithms based on the physics of the atmosphere. GCMs were initially developed from the end of the 1950s on the very first mainframe computers, at first to calculate the weather and, by the mid-1960s, to study climate.

For more than six decades, climate models have kept their original structure while increasing considerably in size – from thousands to millions of lines of computer code. This evolution has been driven by the exponential increase of computing power, by the extension of observation networks, the rise of earth sciences, and by the growing political importance of the climate problem (Weart, 2008). The algorithms of the models have been improved and their spatial resolution increased. Above all, atmospheric circulation models have included more and more phenomena affecting the climate through parametrisations or by coupling with other models. In the 1980s, scientists succeeded in coupling an atmosphere model with a model of the ocean. In the 1990s, climate models gradually encompassed representations of continental surfaces and sea ice and, from the 2000s, aerosols, dynamic vegetation, atmospheric chemistry, land ice and the carbon cycle. Models that include biogeochemical cycles are often referred to as Earth-system models (ESMs). Since the creation of the IPCC, the number of climate models in use around the world has grown enormously – even if the development of climate models and ESMs remains largely restricted to developed countries; see Figure 14.1.

Figure 14.1 Countries with climate models.

In dark grey, countries with climate models listed in AR1 and AR6. In light grey, countries with climate models listed in AR6.

Computer models have greatly contributed to imposing a global vision of climate and climate change (Hulme, 2010), a vision central to the work of the IPCC. The global physico-mathematical vision embedded in these models has thus ousted the plural and geographical conception that prevailed previously – regional climates defined as types of weather (Heymann, 2010). Scientific reasons are often put forward to justify this global scale: for example, carbon dioxide molecules emitted at any point mix quickly with the air and integrate the atmospheric circulation on a planetary scale. But other factors have helped to co-produce this global conception in climate science and policy (Miller, 2004): a powerful infrastructure of observational networks (Edwards, 2010); a long-standing internationally organised scientific community; the huge scientific exploration programs of the American military during the Cold War, relayed by worldwide scientific programs and institutions, such as the World Climate Research Program (WCRP).

GCMs – and later ESMs – are the only simulation tools capable of making quantitative projections of future climate. GCMs were used to assess climate change as a result of increased carbon dioxide atmospheric concentrations long before the creation of the IPCC. In 1979, ‘the Charney report’ for the US National Academy of Sciences first calculated from three models the global warming corresponding to a doubling of the atmospheric carbon dioxide level, while recognising considerable uncertainties (National Research Council, 1979).

Models’ ability to integrate many physical factors when making predictions of future climate have given comprehensive climate modelling a hegemonic status in climate science and, similarly, within the IPCC. But models also contain flaws, gaps and uncertainties (Petersen, [2006] 2012), which modellers attempt to characterise and communicate in IPCC reports (see Chapter 17). To build confidence in their simulations, modellers devote a large part of their work to validating models against observational data. Validating future climate projections poses a particular challenge. There is no a priori guarantee that a model that reproduces the characteristics of the current or past climate will also perform well in predicting future climate (Oreskes et al., 1994). Climatologists have developed multiple strategies to compare simulations and observations in a statistical way (Guillemot, 2010), comparisons that are widely assessed by the IPCC.

14.3 Tools for Science and for Policy

Climate models have always played a central role in the IPCC, starting with the First Assessment Report (AR1) in 1990. Models generate climate change projections, underpin attribution studies and guide regional impact assessments, which form the substance of the report. They validate essential concepts in the climate debate – such as global mean temperature, the climate sensitivity and the global carbon budget. Conversely, and importantly, the IPCC has a major influence on the development of climate models. Thus, the improvement of model parametrisations or the introduction of new components into ESMs takes into account the need for future climate projections that IPCC reports demand. As with academic disciplines – see Chapter 12 – the IPCC is active in shaping the creation of knowledge, via its influence on models, institutions, research programs and careers.

Climate models have a crucial role in predicting, evaluating and attributing anthropogenic climate change, and so the results from climate models inform a range of major policy issues. Social scientists have analysed the effects that both scientific and political objectives have on climate modelling. Because climate change is often framed as a problem in which science is assumed to guide policy decisions, political disagreements are frequently transposed to the scientific field (Pielke, 2002; Sarewitz, 2004). Models have often lain at the centre of such disputes. In the 1990s, debates erupted – especially in the United States – about the difficulties of verifying or validating models in a rigorous fashion (Oreskes et al., 1994). Climate sceptics questioned the scientific credibility of climate models by opposing model simulations to ‘sound science’ based on ‘raw data’. Yet historian Paul Edwards has shown that observed data and climate models are interdependent, this relationship being ‘symbiotic’, with each gaining legitimacy from the other (Edwards, 1999).

Social scientists studied how the political stakes of climate change influence modelling practices, highlighting the elements of co-construction in climate models and simulations. They showed how some parts of climate modelling result from negotiations, or from an anticipation by scientists of the needs of policy makers – notably the representation of uncertainties (Shackley & Wynne, 1996), the estimate of climate sensitivity (van der Sluijs et al., 1998), and recourse to flux adjustments (Shackley et al., 1999).

The hegemonic position of models in climate science – and subsequently in the IPCC – prompted critical analysis of the conception of climate change and the future induced by these ‘global kinds of knowledge’ (Hulme, 2010). In 1991, two Indian scholars criticised the accounting of greenhouse gases based on a physical indicator named Global Warming Potential (GWP). By abstracting these gases molecules from their production context, they claimed, climate models do not distinguish survival emissions of the poor – e.g. methane from rice paddies – from the luxury emissions from the rich – e.g. carbon dioxide from cars and planes (Agarwal & Narain, 1991). According to science and technology studies (STS) scholars, this ‘physico-chemical reductionism’ of climate models obscures the social, economic and historical dimensions of greenhouse gas emissions (Demeritt, 2001). Geographical differences and political contexts are erased. Moreover, models’ hegemony within climate change research ‘reduces the future to climate’ – being partly predictable, climate marginalises other environmental or social factors shaping the future (Hulme, 2011a).

Arguing historically that a ‘culture of prediction’ often gains traction within environmental issues, scholars such as Matthias Heymann have suggested that climate modelling shifted from offering a heuristic approach to understanding climate to offering predictions for decision-making (Heymann & Hundebol, 2017). The central role that models played in IPCC assessment reports was crucial for this shift. Along the same lines, philosophers of science note that due to the multiplicity of processes interacting in climate models, it is almost impossible to link the characteristics of the simulated climate to a particular component of the model. This ‘holism’, they claim, ‘makes analytic understanding of complex models of climate either extremely difficult or even impossible’ (Lenhard & Winsberg, 2010: 253). However, some modellers claim conversely that physical understanding is even more necessary in climate modelling, since the future climate cannot be observed (Bony et al., 2013).

The increasing complexity of climate models is partly a consequence of the need to produce climate predictions. Models have evolved by encompassing more and more environmental phenomena (Dahan-Dalmedico, 2010) because they are supposed to integrate all the processes potentially important for future climate. But climate is subject to a huge range of biogeophysical processes, and the relative importance of any single process is not known until its influence has been tested within the climate system. However, according to some climatologists, this race for complexity, encouraged by a logic of expanded instrumentation and greater funding, should not come to the detriment of research on other climate processes whose role in climate change is known to be essential – for example, concerning cloud feedbacks (Bony et al., 2013).

14.4 A Worldwide Research Infrastructure: CMIP

Since the early 2000s, climate change simulations have been standardised and coordinated through the international CMIP. These multi-model datasets, providing the basis for thousands of peer-reviewed papers, have come to play a prominent role in IPCC reports. In 1990, the WCRP first approved the Atmospheric Model Intercomparison Project (AMIP) in order to compare the output of atmospheric GCMs under similar conditions – same simulation period, same boundary conditions, same carbon dioxide concentrations and so on. Most modelling groups took part in the intercomparison, using the computer facilities of the Lawrence Livermore National Laboratory in California. Having shown the capacity of intercomparison projects to coordinate and organise research (Gates et al., 1999), AMIP paved the way to subsequent ‘MIP’ exercises.

In 1995, the first phase of the CMIP (CMIP 1) coordinated the comparison of 15 atmosphere-ocean coupled models, soon followed by CMIP 2. CMIP 1 and 2 outputs were included in the IPCC’s AR3 report and a few years later, CMIP 3 was designed primarily to provide assessments for the Fourth Assessment Report (AR4), with projections of model simulated climate change under different emission scenarios (Touzé-Peiffer et al., 2020) (see Chapter 15). By 2007, CMIP made outputs from climate change simulations freely available to the scientific community at large, and the simulations for CMIP became synchronised with IPCC reports.

Since 2007, CMIP intercomparison experiments coordinate and pace the work of most modelling groups so as to make it as timely and useful as possible for the IPCC (see Figure 14.2). From CMIP 5 (there was no CMIP 4), the modelling community within WCRP expressed the will to use CMIP to focus not merely on carbon dioxide emissions scenarios, but also on a range of scientific questions. Through an extensive process of consultation across the broad climate community, the simulations comprising CMIP 5 were discussed and prioritised. CMIP 5 included control and historical simulations, climate change scenarios, as well as experiments on regional downscaling, decadal prediction, and a range of ‘idealised’ experiments to help advance understanding of physical processes. CMIP 6 design was also based on a survey amongst climate scientists (Stouffer et al., 2017). Organised under the auspices of the WCRP to support IPCC reports, CMIP has evolved considerably from a few simulations performed by 18 models in 14 modelling groups for CMIP 1, to thousands of simulations performed by over 100 models in 49 modelling groups for CMIP 6.

Figure 14.2 Timeline of AMIPs/CMIPs and IPCC assessment cycles.

The CMIP-standardised dataset allows researchers to align and compare different model simulations and to construct multi-model ensembles of future projections. However, the scientific interpretation of these ensembles is not obvious: an output common to several simulations is not necessarily a guarantee of robustness – it might arise from an error common to all models, and an ‘average’ result is not necessarily more credible than others. More importantly, different models are not fully independent of each other, since they are tied to predecessor versions or else they exchange ideas and codes with other modelling groups. The spread of model outputs does not therefore systematically explore the uncertainty about future climate change (Knutti et al., 2013). Nevertheless, by making it possible to distinguish the patterns common to all models from those that differ, CMIP has made it possible to advance understandings of the multi-model ensemble outputs that now lie at the heart of the IPCC reports.

CMIP has transformed the way climate scientists work by strengthening coordination, encouraging the standardisation of scientific practices, and considerably widening the user community. This would unlikely have happened – or not have happened as quickly – without the presence, and demand, of the IPCC. The free availability of multi-model output far beyond the modelling teams ‘ushered in a new era in climate change research’ (Stouffer et al., 2017). But it also created a growing gap between model developers and model users, who still regard GCMs as a ‘black box’ (Touzé-Peiffer et al., 2020).

14.5 Achievements and Challenges

Today, climate models are rarely called into question in the public sphere, as was still the case as recently as in 2009/10 when climate scepticism was rising in Northern America and Europe (see Chapter 6). Climate models have made it possible for the IPCC to formally attribute global climate change to anthropogenic greenhouse gas emissions. They have shown their ability to reproduce twentieth-century and palaeoclimates, and to produce credible future climate projections, even pre-empting the detection of global warming in climate observations. But now that the IPCC has successfully relied upon climate models to raise awareness of human responsibility for climate change, and pointed to the range of magnitudes of possible future climate change, what is the future role of models in the IPCC?

Two often-cited and growing uses of climate models are for the attribution of extreme climate events to anthropogenic climate change, and for generating climate forecasts at regional or local scales in order to guide necessary adaptations. However, the demand for local forecasts brings into focus the limits of climate modelling. Climate change is more detectable and predictable on large continental scales than on smaller ones: as the spatial scale of climate predictions decreases, uncertainties increase, making it more difficult to distinguish anthropogenic climate change from natural climate variability. Moreover, at local scales, meteorological and social causalities become increasingly intertwined. For example, it can be problematic to attribute to climate change disasters that also arise from socio-political causes, such as social vulnerabilities, inequalities or poor management (Lahsen et al., 2020).

How should models evolve to improve understandings of climate and to better predict future climate? Debates have arisen among modellers. How far should climate models be made ever more complex? Some scholars are considering models that would include ‘human systems’ as an integral part of the Earth system (e.g. Schellnhüber, 1999). Social scientists have criticised this global and systemic vision of modelling the entirety of the planet and of human action. Their argument is that such a vision invites a techno-managerial approach to shaping Earth’s future (Lövbrand et al., 2015), obscuring the multiplicity of cultural values, the inequality of social situations, and the importance of power relations in making decisions.

Other climatologists believe that despite incontestable achievements, the pace of progress in climate modelling is too slow, the uncertainties decrease by too little, and systematic errors remain for many years. Some advocate very high-resolution models (Shukla et al., 2009; Voosen, 2020). But this approach, according to others, does not provide the sets of climate simulations necessary to explore climate variability. Some suggest joining forces to build a unique model from scratch, but others stress the importance of keeping open a diversity of modelling approaches – because of the complexity of the climate system and for fear about the hegemony created by international super-models. Others propose replacing all or part of the model with machine-learning algorithms.

There is no consensus among climatologists about whether GCMs will be able to produce regional quality forecasts, whether they will continue to evolve towards greater complexity, towards very high resolution models, or even towards another type of simulation tool – or even what the place of models will be in future IPCC reports. These debates might seem to be reserved for a handful of climate modellers. But the future of climate modelling will determine much of the future knowledge that will be evaluated and synthesised by the IPCC. The future of climate models therefore concerns not just climate modellers, but decision-makers, policy advisors and, indeed, all people on Earth.

15 Scenarios

Béatrice Cointe

Overview

Scenarios are among the most visible and widely used products of the Intergovernmental Panel on Climate Change (IPCC). Many kinds of scenarios are used in climate research, but emissions scenarios and the socio-economic assumptions that underpin them have a distinct status because the IPCC orchestrated their development. They have evolved from assessment cycle to assessment cycle and serve as ‘boundary objects’ across Working Groups (WGs) and as instruments of policy-relevance. The field of Integrated Assessment Model(ling) (IAM) has emerged to produce these scenarios, thereby taking centre stage within the IPCC assessment process. Because these scenarios harmonise assumptions about the future across disciplines, they are essential tools for the IPCC’s production of a shared assessment of climate research and for ensuring the policy-relevance of this assessment. Yet, the reliance on a relatively small set of complex models to generate scenarios spurs concerns about transparency, black-boxed assumptions, and the power of IAMs to define the ‘possibility space’.

15.1 Introduction

Scenarios are everywhere in IPCC reports, from the climate change projections of WGI (Chapter 14) to the mitigation pathways of WGIII. Often encountered as graphs displaying arrays of roads-yet-to-be-taken, scenarios are in fact complex sets of interrelated numerical variables. Among them, the scenarios projecting long-term evolutions of greenhouse gases (GHG) stand out because the IPCC has orchestrated their development. They are a cornerstone of the IPCC’s outlook on the future. Through them, the IPCC has contributed to the elaboration of a new approach to scenarios, distinct from scenario planning or futurology. This chapter focuses on these scenarios and on the IAMs that produce them.

The IPCC initially produced projections of GHG emissions as input for Global Climate Models (GCMs), but the function of emissions scenarios has greatly increased in scope and ambition. In 2006, the IPCC moved from scenario producer to ‘catalyst’, entrusting the elaboration of new scenarios to the ‘scientific community’ (IPCC, 2006b). Rather than a catalogue of projections, the resulting scenario framework became a toolbox used for various purposes across WGs. This reflects an ambition to integrate the increasingly diverse domains of climate research. As explained in the WGIII contribution to the Fifth Assessment Report (AR5), ‘scenarios can be used to integrate knowledge about the drivers of GHG emissions, mitigation options, climate change, and climate impacts’ (IPCC, 2014a: 48). Their development has harmonised the futures considered by climate research, ensuring some compatibility and comparability across disciplines. It has also accompanied and shaped the emergence and evolution of IAMs, now the main providers of scenarios.

Scenarios are not just outputs of IPCC reports. They are, first, a cornerstone of IPCC assessments and of the broader ambition to construct a consistent and policy-relevant body of knowledge on climate change. They are also a research infrastructure, enabling the organisation, harmonisation and circulation of data across disciplines. Last, they are now a field of research whose emergence was fostered by the IPCC. Considering these three dimensions of scenarios, this chapter first retraces the evolution of IPCC scenarios since the First Assessment Report (AR1). It then clarifies the role of IAMs, and reviews ongoing debates on IAM-produced scenarios.

15.2 The IPCC as Scenarios Producer

To project future climate change, climate modellers need estimates of the future evolution of GHG and other emissions. Providing ‘scenarios of possible future greenhouse gas emissions for the use of the three IPCC Working Groups’ was one of the first tasks undertaken by WGIII in the preparation of the IPCC’s AR1 (IPCC, 1990b: xxxi). Since then, scenario development has gone hand-in-hand with the IPCC assessment cycles. Emissions scenarios have been regularly updated to take into account real-time evolutions in GHG emissions and to meet the evolving needs of climate research and policy.

To date, there have been four generations of scenarios (Table 15.1). They differ in their scope, characteristics and development process (Girod et al., 2009). The first set of scenarios, labelled ‘SA90’, was developed in 1989 by an expert group formed by the ‘Response Strategies Working Group’ (IPCC, 1990b: 17). Its four scenarios were intended as inputs for GCMs (van Beek et al., 2020a).

Table 15.1. Four generations of IPCC scenarios

Assessment cycle	Scenarios	Models used	Development period	Key publications
AR1	SA90 4 scenarios	ASF (US EPA) IMAGE (NL)	1988–1990	Tirpak and Vellinga (1990)
AR2	IS92 (a to f) 6 scenarios	ASF (US EPA)	1991–1994	Leggett et al. (1992) Alcamo et al. (1995)
AR3, AR4	SRES (A1B, A1F, A1T, A2, B1, B2) 6 markers, 40 in total	Open process AIM (Japan) ASF (US EPA) IMAGE (NL) MARIA (Japan) MESSAGE (IIASA) MiniCAM (US)	1996–2000	Nakicenovic et al. (2000)
AR5 onwards	Initially 4 RCPs (2.6, 4.5, 6, 8.5) 5 SSPs (1 to 5) After 2016, 7x5 Scenario matrix (Figure 15.1)	One model for each RCP (selected from the literature): AIM, IMAGE, GCAM, MESSAGE Open process for the SSPs, many models	RCP: 2005–2010 SSP: 2010–2016 Scenario matrix: 2016 onward	Moss et al. (2008) IPCC (2012b) Special issues in Climatic Change (vol. 109, 2011 and vol. 122, 2014) and Global Environmental Change (vol. 42, 2017). O’Neill et al. (2016) for AR6

Source: Author.

The IPCC requested an update in 1991 (IPCC, 1991) and the resulting ‘IS92’ scenarios – standing for ‘IPCC Scenarios 1992’ – were published in a supplement to AR1 (Leggett et al., 1992). As noted in the foreword to the Special Report on Emissions Scenarios (SRES), these IS92 scenarios were ‘pathbreaking’ as ‘they were the first global scenarios to provide estimates for the full suite of greenhouse gases’ (Nakicenovic et al., 2000). The IPCC-requested evaluation of the IS92 scenarios (Alcamo et al., 1995) was possibly even more influential. At the time, there were few emissions scenarios in the literature and no established criteria for their evaluation (Alcamo et al., 1995: 242). The 1995 evaluation set an evaluation framework, recommended good practice, and categorised the potential uses for scenarios. Its guidelines have remained benchmarks for the development and assessment of scenarios.

The ‘SRES scenarios’ were developed between 1996 and 2000 and published in a 600-page Special Report (Nakicenovic et al., 2000). They marked an increase in ambition and scope. Based on an extensive literature review, they were designed for a broader range of purposes and users. The process of constructing the scenarios was also more open, with a 50-author writing team and a call for participation issued to researchers. It produced a set of 6 marker scenarios picked among a total of 40 scenarios, all published in an internet database. One of the main innovations was the development of four storylines to map scenarios along two axes – regional vs. global, economic vs. environmental. With this structuring compass, the SRES scenarios offered a framework for organising and communicating uncertainties surrounding climate change.

The SRES scenarios were used as reference points by all three WGs in the AR3 (2001) and AR4 (2007) reports. By 2003, the scenarios literature had considerably expanded and so the IPCC raised ‘the question of new scenarios for the AR5’ (IPCC, 2003). This initiated a major overhaul of the scenario framework and a redefinition of the IPCC’s role in it.

15.3 The IPCC as Catalyst: Towards a New Scenario Framework

During the revision of the scenario framework, initiated in 2005, the IPCC shifted from being the producer of scenarios to being the catalyst of their production. At its 25th Panel session in 2006, the IPCC delegated the development of new scenarios to the scientific community at large, whilst retaining a facilitating role. The Integrated Assessment Modeling Consortium (IAMC) was founded to coordinate scenario work.¹ The delegation of this work was possible because the emerging IAM community convinced the IPCC chair of its ability to coordinate the process (Cointe et al., 2019). In fact, this community comprised many of the same people involved in previous scenario developments – the three founders of the IAMC included two SRES authors. The process involved IPCC-sponsored meetings (where the main features of scenarios were agreed upon), annual IAMC meetings and a string of research workshops. Reflecting the change of process, there was now not one document presenting the scenarios, but a collection of multi-authored workshop reports, journal articles and special issues (Table 15.1).

The process was bottom-up and had to accommodate the technical specifications of climate models, the requirements of diverse scientific and policy users, the IPCC timeline, and the capacities of existing models. It was guided by two aims: first, to make scenarios suitable for more purposes, especially policy analysis and impact assessments; and, second, to decouple climate change projections from socio-economic assumptions, so as to enable climate modelling, impact studies, and the elaboration of socio-economic scenarios to progress independently in a ‘parallel process’ (Moss et al., 2010).² The resulting framework is quite intricate, and cannot be understood independent of its development process.

Between 2005 and 2017, two types of scenarios were elaborated: Representative Concentration Pathways (RCPs) and Shared Socioeconomic Pathways (SSPs). The RCPs are emissions scenarios leading to specified levels of radiative forcing and designed as inputs for climate models. The radiative forcing profiles serve as a common currency to connect mitigation pathways with climate scenarios. Within the AR5 timeline, four RCPs were selected among published IAM scenarios. They were adapted to the data requirements of climate models (Moss et al., 2008: xv) without harmonising the underpinning socio-economic assumptions. They had to satisfy scientific soundness, requirements from WGI researchers, and expectations for policy-relevance. The choice of the low-emissions pathways illustrates this latter demand. The compatibility of RCP2.6 with the ‘2°C policy objective’ made it a favourite scenario in policy negotiations, but it was only approved after a scientific check (Weyant et al., 2009; Moss et al., 2010; Beck & Mahony, 2018b).

The SSPs, which took longer to develop, provide both narrative (storylines) and quantitative sets of socio-economic assumptions – for example, population and economic growth – that form coherent pictures of how the world might develop without climate change and climate policy (O’Neill et al., 2014). IAMs use these assumptions to project future emissions, combining them with policy assumptions to reach lower emissions levels. In the lead-up to AR6, eight new reference scenarios – combining one SSP storyline with one radiative forcing level – were selected for WGI (O’Neill et al., 2016). This updated the RCPs by expanding their scope and harmonising their socio-economic assumptions.

Rather than a fixed library of scenarios, the new (and current) IPCC scenario framework is a method for organising assumptions in order to harmonise and coordinate different types of climate-relevant projections. This method is encapsulated in the ‘scenario matrix’ (Figure 15.1) designed as a common reference to map the range of assumptions about the future. Thus, contrary to previous versions used by the IPCC, the current scenario framework is an infrastructure to organise model inputs and outputs across research communities, which can be rediscussed, refined and adapted.

Figure 15.1 The scenario matrix combines the five SSP storylines with seven radiative forcing levels.

White boxes: no scenarios available; SSPx-y: scenarios used by WGI in AR6.

Adapted from O’Neill et al. (2016) and Fuglestevedt et al. (2021) (their Figure 1)

15.4 The ‘Mapmakers’: Integrated Assessment Models

The elaboration of the scenario framework established the models used to produce emissions scenarios as a cornerstone of climate research. The emergence of IAMs as a category of models and a tightly bound research community is inseparable from the development of scenarios for the IPCC. The original website of the IAMC emphasised this co-evolution, stating that ‘scenarios to underpin the 1st Assessment Report of the IPCC were elaborated with 1st generation IAMs’ (IAMC, 2017).

IAMs are complex numerical models that represent the interactions between environmental, human and technological systems. They do not build upon a shared theoretical basis, but combine disciplines and intellectual traditions including environmental sciences, systems analysis, macroeconomics and engineering. About 30 IAMs are referenced in the AR5 (Clarke et al., 2014), most of them developed in Europe, the United States and Japan. As tools to assess mitigation trajectories and policy options on a global scale, they constitute an important part of the research assessed by WGIII, especially in AR5 where they were the basis for ‘the exploration of the solution space’ (IPCC, 2014a: ix).

Although IAMs are widely used outside the IPCC scenario process, their emergence is closely tied to the IPCC and its WGIII (see Chapter 12). Corbera et al. (2016) note that a number of WGIII authors have organised their careers around the IPCC, which is the case for several prominent figures of IAM research. Most IAM group leaders have been IPCC authors and have participated in scenario development – some, such as Jae Edmonds, Priyadarshi Shukla, John Weyant or Nebosja Nakicenovic, since the 1990s. The IMAGE model – developed originally by the Netherlands Environmental Assessment Agency (PBL) – has also been a consistent feature of scenario development, except for the IS92.

These links intensified after 2005. The delegation of scenario development to the scientific community, and the central position of IAM-produced mitigation scenarios in the WGIII AR5, drove the organisation and professionalisation of IAM research (Cointe et al., 2019). The combination of an intense schedule of IPCC-sponsored ‘expert meetings’ to work on scenarios, together with several large EU-funded IAM research projects, meant that involved researchers met almost every other month for a few years. This effectively fostered a small and close-knit community. The IAMC, initially created to prepare the RCPs, turned into a disciplinary organisation, and its annual meeting became a fully fledged conference. This emerging community also set up an infrastructure for collaboration and data exchange – partly to be able to work together, partly because it was a requirement for IPCC scenarios. The database created at the International Institute for Applied Systems Analysis (IIASA) to host RCP data now serves as a repository of scenarios for IPCC-related work and for research projects; model documentation and codes are increasingly available; and the IAMC curates a Wiki documenting existing IAMs.

This considerably improves the transparency of IAMs, but it also exposes them to scrutiny and criticism (Robertson, 2021). The prominence of IAM-produced scenarios indeed gives the models’ underlying assumptions, worldviews and solving mechanisms considerable influence in defining the scope of action presented by the IPCC.

15.5 The Contested Influence of IAMs

The position of IAMs-generated scenarios at the interfaces between different domains of climate science and between science and policy puts them at the heart of lively – if mostly academic – debates. These debates highlight the difficulty of disentangling the process of scenario production from the substance of scenarios.

One core issue is the lack of transparency of models. IAMs are complex, interdisciplinary models that are hard to communicate even among experts. They are thus often perceived as ‘black-boxes’ (Haikola et al., 2019). In fact, much of the work undertaken in the IAMC and in modelling projects aims to enable modellers from different groups to understand each other’s models. Transparency about model structure, assumptions and data is necessary to assess the soundness and reliability of IAM projections. This is not only an epistemic concern. Because IAMs-generated scenarios are used to explore the ‘possibility space’, their structure, inputs and underlying assumptions constrain the range of futures brought to the attention of policy-makers (Beck & Mahony, 2018b; Beck & Oomen, 2021; also Chapter 21). According to Robertson (2021), failure to answer calls for transparency risks undermining trust in the IPCC. To some degree, the IPCC has heeded such critiques in expert meetings and publications attempting to tackle the challenge (IPCC, 2017b; Skea et al., 2021).

Criticism of the reliance of IAMs on negative emission technologies (NETs) – and in particular on bioenergy with carbon capture and storage (BECCS) – to achieve scenarios compatible with the 2 °C and 1.5 °C policy objectives of the UN Framework Convention on Climate Change (UNFCCC) has spurred examination of the inner workings of IAMs. This has brought social sciences and science and technology studies (STS) scholars into the discussion (Beck & Mahony 2018b; Haikola et al., 2019; Carton et al., 2020; Low & Schäfer, 2020). These analyses suggest that the tendency of IAMs to favour NETs comes from their representation of technological progress, their focus on least-cost options, and their discounting assumptions. Many limitations of IAMs have been highlighted: they are better at representing technological change than lifestyle changes; they use economics as a basis for decision-making; they tend to consider a limited range of market-based policies; many (not all) are cost-optimisation models; and they hardly consider no-growth or degrowth futures. For critics like Kevin Anderson, this makes them ‘the wrong tool for the job’ (Anderson & Jewell, 2019). However, not all of these limitations are hard-wired into the models, and modellers are reflecting on how to address them (O’Neill et al., 2020; Keppo et al., 2021).

Another issue of concern is the interpretation and use of IPCC-sanctioned scenarios. Scenarios have a life of their own, and their assumptions and limitations often do not travel with them, even when they are acknowledged in the original publications (see also Box 15.1). The performativity of scenarios often escapes their creators. The reason NETs are controversial is that their ubiquity in IAM scenarios makes them seem inescapable – even though these technologies do not exist at scale – to the expense of alternative options, perhaps more realistic but not as frequently modelled by IAMs. NETs-heavy scenarios have thus been criticised for sustaining the discrepancy between policy ambitions and real-world policy action, and for maintaining the chimera that gradual emission reductions can ever be enough (Anderson & Peters, 2016; Beck & Mahony, 2018b; Carton et al., 2020).³

Box 15.1 ‘Business-as-usual’ scenarios

An important choice when making climate scenarios is whether to consider increased climate policy action. Scenarios without additional climate policies, often referred to as ‘business as usual’, serve as baselines against which to assess the effects, costs and benefits of climate action. The SA90 scenarios included policy and no-policy scenarios. As requested by the IPCC, the IS92 and SRES scenarios were all ‘business as usual’. The later scenario matrix is more flexible, but retains the idea of a no-policy baseline: while the SSP storylines do not include climate policies, modellers add policies (usually a carbon price) to reach lower concentrations from the same socio-economic assumptions. The term ‘business as usual’ can be misleading when used to refer to a single scenario. There is not one, but many possible, scenarios without additional policies (Figure 15.1). Scenario experts insist that all can serve as baselines and none should be considered more likely than any other. In practice, however, all are not used equally. Reviewing the use of IS92 scenarios, the SRES report noted that the high-emission IS92a scenario was often used as a baseline, despite explicit recommendations to use the full range of IS92 scenarios for climate assessment (Nakicenovic et al., 2000: 32). More recently, Pielke and Ritchie (2021) and Hausfather and Peters (2020) warned against considering RCP8.5 as a ‘business as usual’ scenario, arguing that its assumptions – especially for future coal consumption – were implausible and outdated. This reignited a longstanding debate about the assignment of probabilities to scenarios to aid interpretation – something that modellers have so far resisted so as not to liken scenarios to predictions (This issue is discussed in AR6; Chen et al., 2021: 109–111.) Rather than ‘mis-uses’, these debates reflect different understandings of the status of baseline scenarios. They highlight the challenges that arise from the use of scenarios as boundary objects and from their appropriation by increasingly diverse users.

15.6 Achievements and Challenges

Since its first report, the IPCC has driven the establishment of scenarios as boundary objects (see Chapter 24) among climate research communities. In orchestrating the development of emissions scenarios, the IPCC has defined an approach to scenarios that puts IAMs centre stage. It has also ‘charted out’ the future. Scenarios work as boundary objects that harmonise assumptions about the future across disciplines, thereby enabling the circulation and comparison of projections.

The development of scenarios has encouraged integration across WGs (see Chapter 18) and supported the emergence of a shared scientific understanding of climate change. Thanks to debates around the new scenario framework, both IAMs and the IPCC scenario infrastructure have become more transparent and open to alternative perspectives. Although there is still much room for improvement, the IPCC is at the forefront of these efforts. Because IAMs are now essential tools for navigating the climate challenge, they are (rightly) held to higher standards of accountability than other models. They need to be subjected to both scientific and political scrutiny.

The opaqueness of IAMs is to an extent irreducible given their complexity and diversity. The intricacy of the scenario framework and the proliferation of scenarios add to the challenge of transparency. However, this opaqueness also stems from the ambition for scenarios to meet the requirements of increasingly diverse users. These users can have different understandings of the usefulness, validity and plausibility of scenarios, a challenge likely to be amplified as scenarios are taken up in political discourses or juridical trials.

Indeed, despite its ambition for comprehensiveness, the scenario framework used by the IPCC offers an incomplete map of the future. Its success has enshrined a quantified, model-based approach largely framed by the requirements of GCMs, at the expense of alternative scenario methods. The next major challenge for the IPCC is to incorporate more diverse and more radical versions of possible world futures into their assessment process.

16 Controversies

Shinichiro Asayama , Kari De Pryck and Mike Hulme

Overview

Over three decades, the Intergovernmental Panel on Climate Change (IPCC) has been no stranger to controversies. Given its institutional character as a boundary organisation working between science and policy, it is no surprise that IPCC reports often reflect wider controversies in the scientific and political life of climate change, especially those concerning its consequences and potential solutions. In this chapter, we explain why controversies about the IPCC’s knowledge assessment are inevitable and point out how the IPCC could use controversies for adapting and developing its assessment processes in constructive ways. That is, we show how controversies serve as ‘generative political events’ for the IPCC’s own learning process. To do so, we classify IPCC knowledge controversies into four types (factual, procedural, epistemic and ontological) and, using two illustrative cases, distinguish between controversies that the IPCC triggers and those that the IPCC absorbs into its knowledge assessment.

16.1 Introduction

Scientific or knowledge controversies do not have a good reputation. They are thought to reveal the uncertainty of scientific knowledge, to undermine the authority of science, and to slow down the quest for ‘universal truth’. It may seem that controversies are best avoided. Yet, in practice, controversies are routine in the production of scientific knowledge. They are important drivers of scientific progress. They are also expressions of the inherent ‘social games’ (Skrydstrup, 2013) embedded in all human activities. In the case of climate change, controversies have been used to discredit the work of climate scientists –and in some cases they are deliberately manufactured for the purpose of stalling policy regulation (Oreskes & Conway, 2010). However, controversies have also contributed to deepening the scientific understanding of climate change – its impacts and potential solutions – and have led to increased transparency and reflection in scientific practices. The Climategate affair that erupted in November 2009 is a good example of this (Raman & Pearce, 2020; see also Chapter 6).

From a science and technology studies (STS) perspective, controversies offer a good entry point for studying the production of scientific knowledge and investigating how science and technology transform society (Pinch, 2015; Jasanoff, 2019). STS researchers may disagree amongst themselves about precisely what constitutes a ‘scientific controversy’. Nevertheless, they would agree that controversies can be regarded as key moments that open the black box of scientific facts and provide a lens through which to explore the solidity (or the fragility) of the institutions that produce scientific knowledge, as well as those who make decisions based on science. By following controversies, researchers are better able to understand ‘science in the making’ and ‘science in society’. As Pinch (2015) points out, it is during a controversy – or a ‘moment of contention’ – that the normally hidden social and cultural dimensions of science may become more explicit. Given that at such moments knowledge claims become subject to public dispute, knowledge controversies can act as ‘generative events’ that create an opportunity to arouse a different awareness of the problem and facilitate the negotiation of new practices and procedures (Stengers, 2005; Whatmore, 2009).

In this chapter, we first look at different types of knowledge controversies that have invested the IPCC, before then highlighting the role of the organisation in both generating and stabilising wider political controversies. In doing so, we view the IPCC as an institution that establishes, stabilises or disrupts the knowledge order about climate change, its impacts and potential solutions (see Chapter 12).

16.2 A Typology of IPCC Controversies

Controversies have been central objects of study in the sociology of scientific knowledge and STS since the 1970s (Pinch, 2015; Jasanoff, 2019). Controversies have become a method by which to study the complex entanglement between science and society. Broadly speaking, controversies are ‘situations where actors disagree’ – that is, they are moments of contention that ‘begin when actors discover that they cannot ignore each other’ and ‘end when actors manage to work out a solid compromise to live together’ (Venturini, 2010: 261). Controversies usually come to an end through the process of ‘closure’, the point in which an agreement emerges.

Controversies can be distinguished from ‘scandals’ or ‘affairs’ – the transgression of values that are dear to a society. Also, a distinction is often made between scientific and political controversies, typically by the different processes of closure. While scientific controversies are considered to be closed through the application of epistemic and methodological standards, political controversies are thought to be resolved by the negotiation of political and economic interests (Pinch, 2015). However, the entanglement between science and society tends to blur this boundary. Controversies are ‘the crucible where collective life is melted and formed’ (Venturini, 2010: 264) such that the science–society boundary is unremittingly constructed, deconstructed and reconstructed during a controversy.

In the context of climate change, scientific controversies rarely remain confined within the scientific domain. Studying controversies therefore facilitates exploration of the underlying dynamics of science and its relations with society (Limoges, 1993; Whatmore, 2009). This does not mean that all scientific controversies spark wider societal disputes. But controversies get particularly ‘hot’ during politically charged situations, for example when the Summaries for Policymakers (SPMs) are approved (see Chapter 20) – or when IPCC conclusions enter public debate.

Below, we classify knowledge controversies surrounding the IPCC into four types according to their ‘origin’ – whether they emerged from factual errors, procedural irregularities, epistemic disagreements or ontological disputes. These types of controversies are not mutually exclusive.

Factual errors: Controversies have occasionally arisen from factual errors contained in IPCC reports. Most prominent was the erroneous statement about the melting rate of the Himalayan glaciers in the AR4 Working Group II (WGII), which surfaced early in 2010. This error gained widespread media attention at the time and, following the 2009 Climategate affair, further fuelled public scrutiny and criticism of the IPCC (Beck, 2012). The controversy led the UN and the IPCC to ask the InterAcademy Council (IAC) to undertake a review of the procedures of IPCC assessment and to make recommendations for change. This controversy was defused by the IPCC revising its procedures and improving its communication practices in response to the IAC recommendations (see Chapter 3).

Procedural irregularities: A second way of characterising controversies that have erupted around IPCC reports are those that have been caused by irregularities – or claimed irregularities – in the IPCC’s own internal procedures. A prominent example is the controversy that followed the AR2 WGI plenary meeting. This concerned the allegation made by climate sceptics against the IPCC that ‘unauthorised’ alterations had been made to the text of WGI’s Chapter 8 on climate detection and attribution after the final IPCC approval plenary had closed, hence violating its own rules of procedure (Lahsen, 1999; Edwards & Schneider, 2001; Oreskes & Conway, 2010). Despite the accusation being unfounded, this Chapter 8 controversy exposed unclear rules of peer review and led the IPCC to formalise its rules of procedure and to add the ‘Review Editor’ role for overseeing the review process (see Chapter 11).

Epistemic disagreements: A third set of controversies arises from disputes amongst scientists and experts about how particular statements about the current state of knowledge should be crafted and communicated. These controversies are grounded in epistemic disagreements within science about how valid, reliable and/or useable knowledge is best generated and assessed. Some of these controversies remain largely contained within the scientific community and the IPCC, like the one regarding projections of future sea-level rise in AR4 WGI (O’Reilly et al., 2012; see Box 12.1). Others, however, have the potential to trigger wider political controversies. For example, calculation of the statistical value of human life in AR2 WGIII led to political conflict between economists and developing country delegations (see Box 16.1). Similarly, the so-called ‘hockey-stick graph’ – used prominently in AR3 WGI – triggered wider disputes both within and beyond the palaeoclimate science community about the reconstruction and representation of millennial scale temperature change (Zorita, 2019). While an iconic figure, the hockey-stick graph is one of the most contested visualisations in the history of climate science (see Chapter 25).

Box 16.1 The controversy over the ‘value of human life’

In July 1995, the IPCC WGIII session in Geneva was in disarray. Government delegations were supposed to approve the AR2 WGIII SPM, but the approval process was stalled due to a bitter dispute over the economic valuation of climate impacts addressed in Chapter 6 of the report (Masood & Ochert, 1995). The authors of this so-called ‘social costs chapter’ had reviewed the literature on the estimated monetary value of the costs and benefits of climate change, including that assigned to human mortality. The ‘value of human life’ number given by the authors became the subject of intense debates because it valued the lives of people in developed nations 15 times higher than those in developing nations. Delegates from developing countries and environmental groups furiously criticised this estimate and called for the chapter to be rewritten or else to be removed entirely (Masood & Ochert, 1995).

The chapter authors refused to revise their calculation, instead defending their approach (Pearce, 1997). They insisted that most attacks against their valuation were rooted in the misreading of what is actually meant by the term ‘value of statistical life’ (VOSL). Notwithstanding the confusing terminology, VOSL was not representing the value of life. It measured people’s attitude to mortality risk – or more precisely, people’s willingness to pay to avoid the risk of death. Because what people are willing to pay is constrained by their ability to pay – i.e., their income – VOSL estimates necessarily vary between rich and poor. For this reason, the chapter authors argued that their regionally differentiated VOSL estimates simply reflected ‘a fact of life’ (Fankhauser & Tol, 1998).

Interestingly, the IPCC authors’ rebuttals revealed how they demarcated ‘science’ (economic valuation) from ‘politics’ (intergovernmental negotiations). Some criticisms were rejected as attempts to ‘hijack an essentially scientific process for political and ideological ends’ (Pearce, 1996: 8). This also points to a difference between economists and general publics in their views on the notion of monetisation. Economists often use money as a common metric for the cost-benefit analysis – a sort of a ‘politically neutral measure of social value’ (Demeritt & Rothman, 1999). Irrespective of the technicality of valuation, however, monetary estimates inherently carry political and ethical implications (Fearnside, 1998). The very idea of monetising human lives was indeed the reason for the moral outrage of developing countries.

A few months later, after the disarray of the Geneva meeting, the AR2 WGIII SPM was nevertheless approved, and WGIII’s Chapter 6 kept intact. But the wording in the SPM was modified to effectively disavow many of its conclusions by stating that ‘[t]here is no consensus about how to value statistical lives or how to aggregate statistical lives across countries. Monetary valuation should not obscure the human consequences of anthropogenic climate change damages, because the value of life has meaning beyond monetary considerations’ (Bruce et al., 1996: 9–10). This change in the SPM was a compromise acceptable to developing nations, but the underlying ethical question about the monetisation of human life remained unanswered.

Ontological disputes: A fourth type of controversy relates not to how questions are answered by the IPCC but, rather, which questions are asked in the first place and by whom (Venturini & Munck, 2021). Here, disputes emerge about the scope of the problems to be assessed by the IPCC and the values and worldviews in which its assessment work is rooted. For example, the IPCC has been criticised for its narrow focus on quantitative modelling analyses and for being heavily dominated by natural science disciplines, i.e., a lack of epistemic plurality (Hulme, 2011b; see also Chapter 12). Similarly, the IPCC is criticised for poorly engaging with indigenous knowledge about the climate (Ford et al., 2016; see Chapter 13). Although these ontological disputes in IPCC assessments are yet to spark public controversy, growing calls for greater ontological diversity might push the IPCC into considering further reforms if it is to address the broader social and cultural dimensions of climate change.

16.3 Triggering and Absorbing Controversies

As well as categorising IPCC controversies according to their origins, another way of looking at knowledge controversies is to examine how IPCC assessments get entangled with wider (geo)political disputes. Here, we can distinguish between the IPCC triggering wider political controversies and the IPCC absorbing external political controversies. To illustrate this, we consider two particular cases from earlier stages in the IPCC’s history. The first is the controversy in AR2 WGIII about the economic valuation of climate change damage – in particular, monetary valuation of mortality risk from climate change (see Box 16.1). The second case is the contested political negotiations over the methodology and accounting rules for calculating forest carbon sinks in the approval of the 2000 Special Report on Land Use, Land Use Change and Forestry (LULUCF) (see Box 16.2).

Box 16.2 The controversy over accounting rules for forest sinks

Within the UN Framework Convention on Climate Change (UNFCCC), the concept of biological sinks from land use activities such as afforestation and reforestation has always been at the centre of political disputes (Fry, 2002). Throughout the 1990s, several developing countries raised concerns that an inclusion of forest sinks in the Kyoto Protocol would be a ‘loophole’ to delay early mitigation efforts. Despite such concerns, the Protocol allowed carbon removals by forest sinks to be accounted for in meeting emissions reduction commitments. This marked the beginning of a long and complex process of political struggle – what Fry (2002) described as ‘twists and turns in the jungle’ – to determine the scope and limit of forest sinks.

Due to a lack of consensual knowledge and no shared normative commitments among negotiating parties – the situation in which Lövbrand (2009) called ‘epistemic chaos’ – the carbon sink negotiations after Kyoto became a tug of war between two opposing political positions (Lövbrand, 2004). On the one hand, a group of industrialised economies including the United States, Canada and Japan viewed sinks as a ‘cost-effective alternative’ to emissions reduction. On the other hand, the European Union (EU), some developing nations and most environmental NGOs considered sinks an ‘obstacle’ to serious efforts to cut emissions from fossil fuels and thus argued for the restricted use of forest sinks. The controversy was so intense that negotiators could not agree on even a simple technical question about the definition of a forest (Fry, 2002).

Under this highly politically charged atmosphere, the IPCC was asked to prepare a Special Report on LULUCF to set the scientific context for the negotiations. Although the IPCC was expected to insert ‘science’ into politics and hence tame the controversy, the IPCC instead became the site of politicised negotiations about forest science (Fry, 2002; Fogel, 2005; Lövbrand, 2009). During the planning and writing of the Special Report, IPCC authors were attacked from all sides. The IPCC plenary discussions on the SPM approval were nearly as intense as the negotiations at the UNFCCC Conferences of the Parties. Every word in the SPM was subject to close scrutiny from government representatives who sought to shape its conclusions (Fogel, 2005).

Notwithstanding the initial expectations, the IPCC Special Report on LULUCF by itself could not end the sink controversy. Due to a lack of agreement on the issue, the COP6 (Conference of the Parties to the UNFCCC) negotiations in the Hague collapsed. However, the US withdrawal from the Kyoto Protocol changed the political landscape of the negotiations. For the sake of ‘saving the Kyoto Protocol’, the EU and those parties critical of forest sinks compromised by agreeing to more generous sink provisions. This led to the adoption of the Marrakesh Accords at COP7 in November 2001, which marked a turning point at which sink negotiations moved from ‘epistemic chaos’ towards ‘epistemic validity’ (Lövbrand, 2009).

Although the approval of the Special Report on LULUCF became the site of a politicised debate, the IPCC’s engagement nevertheless certified the abstract sink concept as a scientifically sound mitigation strategy, contributing to the closure of the controversy (Lövbrand, 2009). And yet, whilst political controversy receded, the ethical question about using terrestrial carbon sinks as a substitute for reducing fossil carbon emissions remained unresolved. This ethical concern over forest sinks has lingered, and recently resurfaced with the increased attention being paid to the role of afforestation for meeting the Paris climate goals (Carton et al., 2020).

The two cases illustrate different ways in which the IPCC became embroiled in political controversies. For the dispute over the ‘value of human life’, the IPCC itself was a trigger for political and ethical contestation among different actors. On the other hand, in the forest sinks dispute, the IPCC was drawn into the controversy by the UNFCCC with an expectation that the IPCC would absorb and defuse political conflict. What these two cases illustrate however is how epistemic controversies within the IPCC are inevitably and intricately bound up with normative disputes in political negotiations within the UNFCCC. At the same time, both cases reveal ethical questions that remained unresolved even after the closure of political controversies. This suggests the likelihood that the IPCC will face similar ethical and ontological controversies in the future.

16.4 Achievements and Challenges

Despite often appearing unwelcome in science, controversies need not always be feared. While sometimes a destructive force, controversies can also act as ‘generative events’ that create new opportunities for organisational learning (Whatmore, 2009). Controversies are likely unavoidable for the IPCC and therefore the management (or at least acknowledgement) of controversy has to be an integral part of IPCC activities.

In order to maintain its epistemic authority amid controversies, the IPCC has tended to engage in ‘boundary work’ (Gieryn, 1995), discursively separating its work from politics and hence maintaining its appearance of ‘policy neutrality’ (see Chapter 21). Through this boundary work, the IPCC seeks to contain scientific controversies within its domain, and at the same time to keep political controversies at bay. However, as seen in the case of the ‘value of human life’ controversy, the IPCC assessment itself can spark intense political controversies. Inversely, as seen in the case of the Special Report on LULUCF, the IPCC can be brought in to pacify political controversies. Scientific and political disputes are thus often inseparable during controversies.

In some cases, the IPCC succeeds in stabilising epistemic controversies and black-boxing scientific facts. As a result, the wider ethical or political disputes from which such controversies emerged – or which they provoked – also reach a point of closure, at least temporarily. Nevertheless, some normative disputes are often not fully resolved and may therefore resurface in other circumstances. The emergence (and cessation) of controversies is always context-dependent.

Given the complex ways in which climate change is embedded in social, economic and political worlds, the IPCC will continue to find itself always positioned on the brink of controversy. There is no easy escape for the IPCC from this exposed position. Perhaps, only through being a learning organisation (see Chapter 6) – constantly revising procedures for knowledge assessment and developing new modes of engagement with diverse audiences – will the IPCC be able to live through moments of controversy. The learning from past controversies might also help the IPCC anticipate issues on the horizon from which unseen controversies might arise in the future.